The present invention relates generally to integrated circuit devices and, more particularly, to an encapsulated, energy-dissipative fuse for use with integrated circuit devices such as a dynamic random access memory (DRAM).
Semiconductor integrated circuits (ICs) and their manufacturing techniques are well known. In a typical integrated circuit, a large number of semiconductor devices are fabricated on a silicon substrate. To achieve the desired functionality of the IC, a plurality of conductors (i.e., metallization layers) are provided to electrically connect selected devices together. In some integrated circuits, conductive lines are coupled to fuses, which fuses may be cut or blown to create an open circuit. For example, in a dynamic random access memory (DRAM) circuit, fuses may be used in conjunction with isolating failing memory array elements and replacing them with redundant array elements. In logic circuits, fuses may also be used to select or modify certain circuit performance or functions.
Laser fusible links are one example of such fuse devices, and are generally formed from conductive lines that can be explosively fused open by the application of laser energy thereto. The applied laser energy causes a portion of the link material to vaporize and a portion of the material to melt. Typically, the fusible link is relatively narrow as compared to the remainder of the conductive structure, and may be composed of materials such as aluminum or polysilicon. Alternatively, a fuseable link may be made of the same metal material as the chip conductors themselves.
In order to intentionally blow such a fuse, a short pulse of laser energy is impinged upon the fuse at a predetermined spot thereon. Since every fuse in an IC is not necessarily blown by design, care is taken to ensure that adjacent fuses are not blown by the applied laser energy. Because of the possibility of laser-induced damage, the areas underlying the fuses are typically devoid of semiconductor devices (e.g., transistors) and the fuses are spaced relatively far apart in conventional systems. Another existing approach to preventing the unintentional blowing of adjacent fuses is to reduce the intensity of the applied laser energy. However, in so doing, it is possible that the fuse material might not completely be ablated or vaporized by the laser. As a result, any fuse material removed by the laser could simply be liquified and then re-solidified, thereby potentially causing a short circuit of an adjacent fuse or device, perhaps even reclosing the very fuse sought to be blown open.
On the other hand, the absorption of excessive laser energy by an IC device may also result in unwanted damage to the IC substrate or to an insulating layer(s) adjacent to the fuse device. With the use of so called “low-κ” (low dielectric constant) materials as insulating layers becoming increasingly common in IC fabrication, there is an increased emphasis on reducing the amount of laser energy needed to blow a fuse, since these low-κ materials are generally more susceptible to laser-induced damage. Accordingly, it becomes a difficult proposition to design a fuse structure which is capable of blowing with lower applied laser energy, but still sufficiently ablates so as not to result in short circuiting of other components.